This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-373524, filed Dec. 28, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an apparatus and a method for data transmission to efficiently transmit multimedia data comprised of a plurality of objects in real time through an information transmission channel in which data errors may occur.
The MPEG-4 method (a method by a standardization group for motion picture compression of ISO/IEC), which is one of international standards for compression of motion picture coding method supports xe2x80x9cobject codingxe2x80x9d to transmit a plurality of objects (visual and audio objects, and the like) after multiplexing. For example, a transmission side transmits one object of moving picture only for persons, and one object only for a background. Then, the receiving side decodes and synthesizes them to display them for reproduction of an image with a person or persons in a background image.
FIG. 1 shows the above flow. The object coding will be described with reference to FIG. 1. Object coding sections 1 are installed for each object. Original data is supplied to the object coding sections 1 and a scene description coding section 2. The object coding section 1 compresses and codes an object such as a moving picture and an audio, to output it as a data stream. The scene description coding section 2 codes a scene description. The scene description is information for reproduction of the objects which are compressed and coded at the object coding sections 1 as one scene. The outputs of the object coding sections 1 and the scene description coding section 2 are multiplexed at a multiplexing section 3. The multiplexed data is transmitted to the receiving side through a data transmission channel 8.
At the receiving side, the multiplexed data is demultiplexed to coded data of objects and scene description by a data demultiplexing section 4. The coded object data and the scene description are separately processed. Object decoding sections 5 decode the coded object data. A scene description decoding section 6 decodes the coded scene description. A scene synthesizing section 7 synthesizes the object data from the object decoding sections 5 for reproduction, based on the scene description from the scene description decoding section 6.
In a conventional device having the above configuration, the object coding section 1 compresses and codes object data such as moving picture and audio. Each coded object data is made into stream, which is called as an elementary stream.
The scene description coding section 2 codes a scene description for reproduction as one scene by synthesizing the objects. The data multiplexing section 3 multiplexes data from the object coding sections 1 and the scene description coding section 2 to transmit them through the data transmission channel 8 as one stream. The data received through the data transmission channel 8 is supplied to the data demultiplexing section 4, which demultiplexes the multiplexed data into the coded data of objects and scene description. The coded data of objects are supplied to the object decoding sections 5, and the scene description to the scene decoding section 6.
The object decoding section 5 decodes the coded object data to supply the object data to the scene synthesizing section 7, and the scene description decoding section 6 decodes the coded scene description to supply the scene description to the scene synthesizing section 7.
The scene synthesizing section 7 synthesizes scenes for reproduction of images, based on the object data from the object decoding sections 5 and the scene description from the scene description decoding section 6. The scene description denotes priority of the elementary stream corresponding to each of individual objects.
The priority is given to the objects according to production intention of an author who produces a multimedia content. For example, the priority is given to an object which the author looks upon as an important one, or to object with greater importance, as an object of persons generally has greater importance than those of backgrounds.
On the other hand, in wireless communication, there have been some cases where a mechanism to guarantee completeness of the data is introduced in the lower layers of a communication protocol such as a physical layer and a data-link layer by using a method through which detection of error at the receiving side causes request for re-transmission from the receiving side to the transmission side and the transmission side retransmits the data responding to the request when a transmission channel with high possibility of data errors such as wireless communication is used.
However, the above method may not be applied to communications which require real-time transmission such as MPEG-4 of so-called stream data as one of important factors, since there is a serious problem such as a time lag required for the re-transmission.
There are increased possibility to cause pauses in reproduction of moving picture and audio at the receiving side due to time lags for the re-transmission, though it is important to maintain real-time transmission in the transmission of the stream data. The pauses in the moving picture and audio become degradations in application qualities themselves.
Thereby, in general real-time communication of multimedia data, it has been usual not to perform re-transmission of data at the physical layer and the data-link layer even with possible loss of the completeness of the data, except when there are remarkably many errors in the transmission channel. Therefore, there may be a case where a part of data are not transmitted.
On the other hand, there has been a method to protect information by forward error-correction (FEC) where transmission is performed by adding redundant information to original information, considering possible errors in the upper layers. For example, the method is found in a xe2x80x9cH.233xe2x80x9d standard, as a typical protocol for multiplexing and demultiplexing in videophone application. In xe2x80x9cAnnex Axe2x80x9d, xe2x80x9cAnnex Bxe2x80x9d, and xe2x80x9cAnnex Cxe2x80x2xe2x80x9d, and xe2x80x9cAnnex Dxe2x80x9d of the xe2x80x9cH.233xe2x80x9d standard, information is defined to be protected based on the FEC.
However, as there is no consideration of contents of data to be transmitted for xe2x80x9cprotection of informationxe2x80x9d in the above standard, the same error-correction information is uniformly added to all data without consideration of the importance of each data. Then, data with greater importance, and those with less importance have the same error rate. But, as the real-time transmission is an important factor, and objects have their own importance, in the MPEG-4, it is useless to perform the error-correction coding with the same level of error-correction for every object, and there may be a case to lose the real-time transmission. Therefore, the resources are not effectively used.
Accordingly, it is an object of the present invention to provide an apparatus and a method for data transmission, in which it is possible to effectively use the resources, maintain the real-time transmission of data, and prevent degradation of transmitted data by changing the level of the error-correction according to the importance of object, and performing the error-correction coding for the objects according to the importance.
According to the present invention, there is provided a data transmission apparatus for transmitting data comprising a plurality of objects having respective priority, the apparatus comprising means for selecting an error-correction coding method for each of the plurality of objects based on the priority of each of the plurality of objects, means for error-correction coding of each of the plurality of objects using the selected error-correction coding method, and means for multiplexing plurality of coded object data and transmitting multiplexed data through a transmission channel.
According to the present invention, it may be possible to further comprises means for detecting a traffic quality of the transmission channel, and said selecting means may select an error-correction coding method based on the priority of each object and the traffic quality.
According to the present invention, there is provided a data reception apparatus for receiving coded transmission data comprising a plurality of coded object data, each object having a priority, the apparatus comprising means for receiving and demultiplexing the coded transmission data into the plurality of coded object data, means for detecting the priority of each object, and means for error-correction decoding of each of the coded object data based on the priority detected by said detecting means.
According to the present invention, there is provided an object coding apparatus for transmitting data formed of a plurality of object data and scene description data, each object having a priority, the scene description data indicating the priority of each object and how the object data are synthesized, the apparatus comprising means for determining error-correction coding methods for the plurality of object data respectively based on the priority, means for error-correction coding of each of the plurality of object data using the determined error-correction coding methods, means for error-correction coding of the scene description data using a predetermined error-correction correction coding method, and means for multiplexing coded scene description data and a plurality of coded object data and transmitting multiplexed data.
According to the present invention, there is provided an object coding/decoding system comprising means for determining error-correction coding methods for the plurality of object data respectively based on the priority, means for error-correction coding of each of the plurality of object data using the determined error-correction coding methods, means for error-correction coding of the scene description data using a predetermined error-correction coding method, means for multiplexing coded scene description data and a plurality of coded object data and transmitting multiplexed data, means for receiving and demultiplexing the multiplexed data from said object coding apparatus into the coded scene description data and the plurality of coded object data, means for detecting the priority of each object from the coded scene description data, means for error-correction decoding of each of the plurality of coded object data using a decoding method based on the priority detected by said detecting means, means for error-correction decoding of the coded scene description data using a predetermined decoding method, and means for synthesizing plurality of decoded object data based on a decoded scene description.
According to the present invention, it is possible to effectively use the resources, maintain the real-time transmission of data, and prevent degradation of transmitted data by changing the level of the error-correction according to the importance of object, and performing the error-correction coding for the objects according to the importance.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.